Generally, a tube is provided in a steam boiler or a heat exchanger, and one end of the tube is inserted into a hole formed in a tube-sheet (“tube-hole”, hereinafter), and fixed therein. In many cases, the tube is fixed to the tube-sheet in the following manner as shown in FIG. 4. That is, a tube-hole 2 is formed in a tube-sheet 1, and an end of a tube 3 is inserted into the tube-hole 2. The tube 3 includes a region 3b including an inserted portion 3a located in the tube-hole 2. A diameter of the region 3b is increased so that the inserted portion 3a is fixed to the tube-hole 2. A tip end of the tube 3 is flared to form a flare portion 3c. 
Diameters of diameter-increased portions 3d and 3e are increased as compared with an inner diameter of the tube-hole 2 by a diameter-increasing operation. The diameter-increased portions 3d and 3e are formed outside of the tube-sheet 1 in many cases. Further, as shown in FIG. 5, one or more annular grooves 4 are formed on the inner circumference of the tube-hole 2, and when the diameter-increasing operation is carried out, a diameter-increased portion 3f is generated at a location corresponding to the groove 4, thereby establishing stronger engagement in many cases.
When the tube 3 is rusted or damaged, it is necessary to pull out the tube 3 from the tube-sheet 1 and replace the same. A conventional method for pulling out the tube 3 is as follows. That is, the inserted portion 3a which is diameter-increased and fixed is rapidly heated by a gas torch or induction heating from the inner side, the inserted portion 3a which trends to thermally expand is restrained by the inner circumference of the tube-hole 2 to bring the inserted portion 3a into a compressive yield state, and after the inserted portion 3a is cooled, the diameter thereof is reduced (heating and diameter-reducing operation) to loosen the inserted portion 3a with respect to the tube-hole 2 and then, the tube 3 is pulled out into a direction of the arrow A or B.
When the tube 3 is pulled out, a portion of the tube 3 is cut off at an appropriate right side location (in FIGS. 4 and 5) from the tube-sheet 1, besides, when the tube 3 is pulled out in the direction of the arrow A, since the flare portion 3c or the diameter-increased portion 3d is caught by the tube-hole 2, these portions are ground by a grinder, or flare portion 3c is divided in circular direction to three petal-like portions by gas torch-cutting without damaging the tube-sheet and then shrunk by hammering. When the tube 3 is pulled out in the direction of the arrow B, since the diameter-increased portion 3e is caught in the tube-hole 2, the same operation is carried out for the diameter-increased portion 3e. 
However, the diameter-reducing ratio of the inserted portion 3a by the aforementioned heat-and-cool loosening operation is about 1% at the most, and in the operation it is necessary to restrain the outer surface of the tube, and thus, when the groove 4 is formed on the inner circumference of the tube-hole 2 as shown in FIG. 5, the diameter of the diameter-increased portion 3f existing in the groove 4 is not reduced so much, and it is almost impossible to reduce its diameter to a value smaller than the inner diameter of the tube-hole 2. For this reason, according to the structure having the groove 4, the diameter-increased portion 3f is caught in the side wall of the groove 4 and the diameter-increased portion 3f can not be pulled out in many cases.
In such a case, the region 3b of the tube 3 whose diameter is increased is divided in the axial direction of the tube by gas torch cutting and then is shrunk by the hammer or the like, and thus, the operation becomes complicated, and there is a problem that the tube-sheet 1 is damaged at the cutting in many cases, and high costs are required for repairing the damage. Further, when the flare portion 3c or the diameter-increased portions 3d and 3e are ground or cut, there is a problem that the tube-sheet is damaged in many cases and high costs are required for repairing the damage.
As a method for solving such problems, the present assignee has developed a method for pulling out the tube from the tube-sheet (see Patent document 1). In this method, a narrow section of one end of a region of the tube whose diameter is increased is heated into a red-hot state, and a tractive force is applied to the tube end, thereby tensile-yielding the narrow section in the red-hot state to reduce its diameter, and the same operation is carried out for the adjacent narrow sections, and the same operation is repeatedly carried out while moving the positions of the red heated narrow sections one after another, thereby reducing the diameter substantially of the entire diameter-increasing region including the diameter-increased portions 3d, 3e and 3f to pull out the tube from the tube-sheet (Patent document 1). According to this method, it is possible to increase the diameter-reducing amount, and there is a merit that the tube can easily be pulled out. However, this method has a demerit that since the operation for red-heating the narrow section to cause the tensile yield and to reduce the diameter is carried out repeatedly while changing the positions, the much labor is required for the operation and it takes time for the operation.
Japanese Patent Application Laid-open No. H8-229749